1. Field of the Invention
The present invention relates to a semiconductor device, and particularly relates to a semiconductor device having a multilayer wiring structure using Cu wiring.
2. Description of the Related Art
In recent years, a technique on a wiring process has become increasingly significant for high-speed operating semiconductor integrated circuit devices (LSIs) as the LSIs become highly integrated. This is because disadvantages of a signal transmission delay have become noticeable as semiconductor elements become finer. To suppress an increase of the signal transmission delay, lower resistance of wiring, and a reduction of a capacity between wirings and a capacity between wiring layers are necessary.
As to attaining low resistance of the wiring, a semiconductor device using a copper (Cu) wiring having lower resistance comparing with that of a conventionally used aluminum alloy wiring has been practically used. Also, as to a reduction of a capacity between wirings and a capacity between wiring layers, an insulation film having a low relative dielectric constant (a low dielectric constant film) comparing with that of a silicon oxide used conventionally as an interlayer insulation film has been studied, and introduction of a multilayer wiring technique using a Cu wiring and a low dielectric film has been studied.
Here, since Cu is a material having a very high diffusion coefficient, to prevent diffusion of Cu from a Cu wiring to an interlayer insulation film on the Cu wiring, it is necessary to provide a diffusion prevention insulation film on the interlayer insulation film provided with the Cu wiring in a state of covering the Cu wiring.
As the diffusion prevention insulation film, silicon nitride (SiN) having a Cu diffusion prevention function and a relative dielectric constant of 7 or so and silicon carbonitride (SiCN) having a relative dielectric of 5 or so are used. For example, an example of a semiconductor device, wherein a Si enriched lower layer silicon nitride based insulation film having high adhesiveness with a Cu wiring and an upper layer silicon nitride based material film having a stoichiometric composition are stacked as diffusion prevention insulation films on an interlayer insulation film provided with the Cu wiring, has been reported (for example, refer to the Japanese Unexamined Patent Publication No. 2000-183059).
However, in a semiconductor device as above, a relative dielectric constant of a diffusion prevention insulation film is high, so that it is necessary to lower the dielectric constant not only of the interlayer insulation film but of the diffusion prevention insulation film to reduce the capacity between wiring layers as the semiconductor device becomes finer. However, when the dielectric constant of the diffusion prevention insulation film is made lower, film density of the diffusion prevention insulation film becomes low, so that a surface reaction with the Cu wiring becomes weak and adhesiveness of the diffusion prevention insulation film and the Cu wiring declines. Consequently, voids arise as a result that Cu easily moves and disadvantages of declining the wiring reliability arise, such that electro migration (EM) resistance and stress migration (SM) resistance decline.
Also, as a result that the film density of the diffusion prevention insulation film declines, there is a disadvantage that oxygen and water from the air or the interlayer insulation film provided as an upper layer of the diffusion prevention insulation film permeate the diffusion prevention insulation film, and the Cu wiring as the lower layer is oxidized to increase the wiring resistance. Furthermore, due to a decline of the film density, it is liable that strength of the diffusion prevention insulation film itself declined and resistance properties, such as time dependence on dielectric breakdown (TDDB), decline.